Inflammation has several characteristic processes including permeability changes in the microvasculature, leakage of the elements of blood into the interstitial spaces, and migration of leukocytes into the inflammed tissue. Chemotactic factors are liberated at the site of inflammation and phagocytic leukocytes (neutrophils) migrate into the area, secreting lysosomal constituents. In addition, to releasing lysosomes, neutrophils exhibit aggregation and superoxide generation when exposed to appropriate stimuli. Neutrophil aggregation has been characteristically associated with inflammation.
A class of compounds known as nonsteroidal anti-inflammatory drugs (NSAIDs) has been widely used to combat inflammation as such drugs do not display the undesirable side effects of the steroidal anti-inflammatory agents. The most common member of this class is aspirin. One of the properties of NSAIDs is their ability to inhibit the aggregation of human neutrophils. Measuring the degree of neutrophil aggregation inhibition caused by these anti-inflammatory agents is a method of screening potentially therapeutic compounds for effectiveness as anti-inflammatory agents because neutrophil aggregation is a characteristic feature of inflammation (the degree of aggregation being proportional to the intensity of inflammation). However, it is difficult and impractical to measure aggregation inhibition of neutrophils directly because the procedure requires the isolation and purification of neutrophils from whole blood, a multistep process which is both time and labor intensive. Moreover, sterile techniques must be used. The procedure requires separating neutrophils from venous anticoagulated blood by sequential Hypaque-Ficol gradient centrifugation, dextran sedimentation, and hypotonic lysis of residual red blood cells.
Therefore, it is desirable to utilize an in vitro model for neutrophil aggregation which can be utilized very economically in time, effort and expense but which also yields reliable results. It is desirable to work under non-sterile conditions. This saves time and labor.